This invention relates to an induction system for internal combustion engines and more particularly to a compact, high efficiency induction system.
It has been proposed to increase the power output of an internal combustion engine for a given engine displacement through the use of a supercharger. Most superchargers, and particularly those of the centrifugal type, do not generate any significant boost at low engine speeds. This is particularly true if the supercharger is of the exhaust turbine driven type (turbocharger). Since the supercharger is positioned in the induction conduit that supplies the chambers of the engine, the air flow across the supercharger at low engine speeds causes a restriction which may in fact decrease power output when the supercharger is not delivering any significant boost.
In order to avoid the aforenoted difficulties, it has been proposed to provide a valved bypass around the supercharger so that the air may be inducted directly into the engine without passing across the supercharger impeller during period when the supercharger is not delivering any significant boost. Systems of this type have employed pressure responsive valves for controlling the amount of bypass and these valves have been conventionally of the poppet or butterfly type. There are several disadvantages, however, to the use of such valves. Poppet valves are heavy and have relatively large inertia so that they fail to be sufficiently responsive to sudden changes in running conditions, as may readily occur in conjunction with this type of engine. The butterfly type valve has the disadvantage that its position may fluctuate due to engine vibrations and the normal pulsations which occur in an induction system.
It is, therefore, a first object of this invention to provide an improved supercharger bypass system for an internal combustion engine induction system.
It is another object of this invention to provide a bypass valve for a supercharged engine induction system that is more responsive to changes in running condition and less prone to vibrations.
In induction systems embodying superchargers and valved bypasses, it is normally the practice to employ a pressure responsive valve that controls the flow through the bypass. As is well known, however, the pressure in the induction system varies considerably during the running of the engine due to the alternate opening and closing of the intake valves or intake ports of the engine. Such pulsations can cause the pressure responsive valve to open and close at periods when such movement is neither desirable nor necessary. In addition, the effect of the pulsations on the valve element can very well subject it to greater wear than normal and, accordingly, predetermine failure. This is particularly true if a reed type valve is employed.
It is, therefore, a still further object of this invention to provide an improved bypass system for a supercharged engine wherein the valve is not subjected to vibration or pulsations in the intake system.
In addition to the pulsations in the induction system caused by the opening and closing of the inlets, the output of the supercharger, particularly if it is of the turbocharged type, also can cause variation in the pressure outlet. The same pulsation which occur in the intake side of the engine are also present in the exhaust side and can cause pulsations in the driving force of the turbocharger. These pulsations will affect a pulsating output of the compressor stage of the turbocharger which can deteriorate engine performance.
It is, therefore, still a further object of this invention to provide a supercharged induction system wherein pulsations in the output of the supercharger are isolated from the intake ports of the engine.
In induction systems that employ valved bypasses around the supercharger, it has been the practice to employ a valve member that is normally biased to a closed position. When the engine is operating under the condition that the supercharger is not generating any significant boost and unsupercharged air is delivered through the bypass, this means that the valve must be urged to an open position by the pressure difference across the induction system. Obviously, this adds a further restriction to the induction and can offset the advantages intended to be accomplished by the bypass.
It is, therefore, still a further object of this invention to provide an improved efficiency bypass type induction system for a supercharged internal combustion engine.
In conjunction with engine induction systems, it is the normal practice to provide an air cleaner that filters the intake air. In connection with certain forms of induction systems and particularly those which serve some of the objects aforenoted, it is desirable to provide a plenum chamber in the induction system between the air inlet and the individual intake ports of the engine. In certain vehicle applications such as in motorcycles, the size of the vehicle does not afford the opportunity to permit the incorporation of separate air cleaners, plenum chambers and the like.
It is, therefore, a still further object of this invention to provide a compact, combined air cleaner, plenum chamber device for the induction system of an internal combustion engine.
As has been noted, the induction system of an engine experiences uneven flow due to the sequential opening and closing of the intake valve or the intake port. Because of the stopping and starting of the intake charge, charging efficiency can deteriorate, particularly at low speeds when these effects are more pronounced. It has been proposed to employ a check valve in the intake passage of such an engine to improve the charging efficiency. However, since the area between the check valve and the intake port is normally quite small, the inertial energy of the intake air that is reserved by the use of the check valve is relatively insignificant. If, on the other hand, a large volume is provided upstream of the intake valve, the response time under acceleration can be significantly deterred since a larger volume of the air must be accelerated during abrupt throttle openings.
It is, therefore, a still further object of this invention to provide an induction system for an internal combustion engine wherein the charge efficiency of the engine is improved throughout the engine speed range without deteriorating responsiveness to rapid accelerations.